1. Field of the Invention
The present invention relates to a process for producing a water-soluble polysaccharide, and more specifically, it relates to a process for producing a water-soluble polysaccharide excellent in its dissolution behavior, and in suppression of foaming and dusting during its dissolution.
2. Description of the Related Art
When a water-soluble polysaccharide is dissolved in or dispersed into water, it has had useful effects such as the so-called dispersion effect of improving the dispersibility of other substances, the so-called thickening effect of increasing the viscosity of the system and an emulsifying effect, and it has shown various useful functions and properties.
Many of the water-soluble polysaccharides are often in the form of dried powder products. When the powder products are added to water, they are hydrated more quickly, on their surface contacted with water, than they are dissolved therein while they are being dispersed thereinto. They have therefore the problem in that they produce so-called "undissolved powder lumps" which are difficult to dissolve. That is, since many of the water-soluble polysaccharides exhibit thickening behavior and are capable of lowering the surface tension, they have problems such as mentioned below. When they are added to water, to be dissolved therein, they tend to generate foam and, in extreme cases, the volume of the foams becomes larger than that of the aqueous solution, which requires enlargement of the dissolution installation. Moreover, when "undissolved powder lumps" exist in the foam thus generated, dissolution of the "undissolved powder lumps" is very difficult.
In order to efficiently dissolve such water-soluble polysaccharide powder which is difficult to dissolve in water, there are procedures such as a procedure in which stirring is conducted under reduced pressure, a procedure in which the water temperature is raised or the water is heated during dissolution, and a procedure in which a dissolver of a centrifugal defoaming type is used. However, any one of these procedures requires a corresponding facility. Accordingly, a water-soluble polysaccharide in a commercial form, in which the polysaccharide is readily dissolved in water, is desired.
Moreover, in order to suppress foaming during dissolution of the water-soluble polysaccharides in water, there has been a procedure of adding an antifoamer. However, the procedure requires repeated operations; therefore a water-soluble polysaccharide which foams less is desired.
Furthermore, since many of the water-soluble polysaccharides are in the form of dried fine powder, the polysaccharides tend to float in the air at the time of handling them, that is, so-called "dusting" tends to take place; in extreme cases there arises not only the danger of dust explosion but also a sanitary problem in that the operation environment is polluted.
In order to prevent such dusting of the water-soluble polysaccharides, there is a procedure in which the particle size is increased in the granulating step and a procedure in which the particle surfaces of the powder are processed. However, since the granulation and surface processing steps become costly, the steps are difficult to adopt as mere countermeasures for the powder floating.
As explained above, in order to make the water-soluble polysaccharides exhibit their functions and properties, it is essential to dissolve them in or disperse them into water. However, the water-soluble polysaccharides in powder form have the problem of dissolution in water as well as that of foaming during dissolution and dusting during the handling operation. Accordingly, they are not necessarily satisfactory at present from the aspect of handling.